The ground system is a set of conducting elements of a specific electrical system, which do not have interruptions and which connect the electrical equipment to the terrain or a metallic mass. It comprises the ground and the equipotential network of wires that normally do not conduct current.
In general, every electrical installation, from the generation, transformation, transmission, distribution, to the final user, must include a ground system, for protecting the equipment and the people from surges and electric shocks.
The main functions of the ground system are: guaranteeing safety conditions to living organisms, allowing the protection equipment to clear failures quickly, serving as a reference to the electrical system, conducting and dissipating the leakage, electrostatic and lightening flash currents with sufficient capacity, transmitting half wave and long wave radiofrequency signals and making a low resistance connection to the ground and with reference point of the equipment (Internal Regulations for Electrical Installations, RETIE, Ministry of Energy and Mines, Colombia, Apr. 2, 2007, Article 15).
In the aerial systems of electric energy distribution in Medium Voltage (for example, 34500 Volts, 13200 Volts or 11400 Volts), where there are voltage transforming elements or transformers, a strongly grounded system must be guaranteed for the protection of the equipment. In turn, the aerial networks of low voltage commonly have multigrounded systems with installation of uniform ground leads, for example, each 3 or 4 spans ahead, depending on the values of reactance and resistance typical of the circuit.
Said ground system must have a suitable lead that, in case of a failure, guarantees that there are no by-pass voltages (potential difference existing between two points of the surface of the terrain, separated by a distance of about one meter), contact voltages (potential difference existing between a grounded metallic structure and a point of the surface of the terrain by a distance of a meter) or transferred voltages, exceeding the thresholds that can be tolerated by a human being.
The ground system traditionally used in the electrical distribution network uses as ground lead a copper wire, which is installed to the exterior of the pole with different elements and accessories for subjection. FIG. 1 illustrates the traditional system of ground lead in which the copper wire (50) introduced into a galvanized steel tube (52) is installed in the exterior of the pole (54), through the use of steel braces (51). The use of the galvanized steel tube helps protecting the ground lead wire, and isolates it avoiding a possible contact voltage.
This type of ground system requires the additional assembly of elements after the installation of the pole, which implies an increase in the time and cost of the installation. In addition to the above, the elements of the system are exposed, contributing to visual contamination, and being easily prone to stealing, which implies extra costs for the replacement of the ground system, and possible damages in electrical and electronic equipment installed on the poles (when it is the case), or malfunctioning of the electric system causing a loss in the continuity of the service.
An explored alternative to solve this problem has been installing the ground lead inside the inner cavity of the pole. In this type of system, the lead may or may not be introduced in a galvanized steel tube, and in the upper and lower section of the pole two orifices are used, through which the lead wire passes and the connections to the system and the ground electrode are made. However, this system also requires extra time after installation, the use of additional elements to fix the lead and the lead wire is exposed in the upper and lower sections of the pole, prone to stealing. Field tests performed in distribution systems have demonstrated that, in the ground systems where the lead is introduced in the inner cavity of the pole, said lead has been easily stolen.
The patent document JP2006296113 discloses a ground method that allows leads not to protrude of the surface of the pole. Said method consists in using distribution poles including a longitudinal groove in their surface, through which the leads pass. In this manner, the leads are less exposed, being easier to perform works on the pole in service. However, although this system avoids an excessive protrusion of the leads in the surface of the pole, said lead is exposed, requires additional fastening elements and is likewise anyways, prone to extraction.
Therefore, in the technical field, there is a need for providing a safe and efficient ground system for electric energy distribution poles, which does not imply additional steps in the pole installation and that effectively prevents the extraction of the lead.